Windows 8 shutdown when computer put to sleep

This is a tough one and my search skills are hitting a brick wall. I have installed Windows 8 on an existing Elitebook. After use, I will put the computer to sleep (either by closing the lid, as I specified in Power Settings; or by going to the Charms settings and choosing Sleep).

Some time later, like the next day, I will try to resume from sleep, only to find the computer has actually shut down. I checked battery settings - the battery has a full charge, and everything else in the Power Settings to see if I'm specifying shut down, but nothing stands out.

I am seeing similar behavior, but you likely have a setting to put the computer into hibernate or shut down after a few hours under the advanced power options for your power plan. I never bothered looking for the reason personally since resuming from that state on a SSD is about as fast as resuming from sleep. I'm using the default settings on the balanced power plan by the way, my Windows 8 laptop is currently tucked away safely and I'm not really feeling like pulling it out to check the exact settings, sorry.

No, that's not hybrid sleep. Hybrid sleep isn't turned on by default on laptops since when the feature was introduced, most laptop storage drives were still HDD instead of SSD and no one wants an HDD spinning while attempting a sleep since the most common activity for a laptop going to sleep is also being moved into bag/desk/floor/etc.

This is just a simple passing into hibernate after a set time. Hybrid sleep is making a hibernate image, then going to sleep. If the computer loses power while sleep, it can restore from the hibernate image. It's only turned on on desktops by default.